Convergence testing is an eye exam that assesses the ability of the eyes to coordinate or work together and focus on a near target. Convergence is an individual's ability to roll or move their eyes inward towards each other to look at an object up close. It is a critical component of visual functioning that enables a distinct binocular vision when viewing a very close object. Convergence develops early in life and enables a child to establish stereopsis or 3-D vision and explore their environment.
Weak convergence or convergence insufficiency (CI) is a condition in which the eyes can't work together when looking at objects up close. It is a common binocular vision disorder among school-age children, young adults and contact sportspeople. CI may cause one or both of the patient's eyes to deviate outward, resulting in vision-mediated functional difficulties and visual discomfort. It can lead to decreased attention and slowed reading, which may impact work, academic, and sports performance.
If not treated or poorly treated, the condition can persist into adulthood. CI affects between two and thirteen percent of the US population. It is the leading cause of common complaints such as headaches, eye strain and blurred vision.
Near point of convergence (NPC):
This is the standard test for convergence ability. It is a measure of pursuit convergence, the point at which the visual axes cross each other under the highest effort of the confluence.
A qualitative measurement of the convergence leaps from distant to a near target point.
The convergence testing can be done at the doctor's office, eye clinic, or hospital by:
- An ophthalmologist
- An optometrist
- An orthoptist
Often, patients with convergence insufficiency go undiagnosed because they may seem to have normal vision. The patient needs to inform the doctor if they experience difficulties with learning or reading. The doctor can diagnose CI by taking the patient's medical history, performing a routine eye exam and convergence testing.
The causes of CI are not yet known. They may include:
- Neurodegenerative diseases
- Traumatic brain injury
- Certain medications
- Myasthenia gravis
- Graves' disease
Researchers also suspect that the condition may be hereditary and runs in families. The doctor will have an extra interest in a patient who has a relative with CI. People who use the computer for extended periods are also at an elevated risk.
The condition can exhibit different signs and symptoms for every patient. In some cases, there are no symptoms. The common signs and symptoms include:
- Rubbing, squinting, closing or covering an eye
- Problems with motion sickness and vertigo
- Trouble remembering what was read
- Tired watery eyes after a near/far task
- Sleepiness during the activity
- Frequent loss of place
- Short attention span
- Difficulty reading
- Vision problems
Preparation & Expectation
Convergence testing doesn't require any special preparation.
The steps involved will depend on the technique:
Near point of convergence test
It is a simple test that only uses a ruler and a fixation target. The patient will sit down in a chair in a well-illuminated room. The doctor will ask the patient to look at the fixation object placed approximately 50 centimeters before them at the nose level. S/he will observe any changes in eye movements.
The doctor will move the fixation object smoothly and slowly close to the nose of the patient and ask the patient to report when the fixation object appears double. S/he will then move the object away from the patient's eyes until the eyes begin to fixate on the object. The doctor may repeat the test just to be sure the patient understands and follows the procedure. Where the patient has weak convergence, the NPC of the repeated tests will be different from the earlier readings.
It is an additional test for patients suspected to have CI and is more reliable for a near viewing scenario. It uses a Brock string or a Dot card. The patient sits down in a chair in a well-illuminated room. The doctor will place the card at the patient's nose level. S/he will proceed to note any changes in the patient's eye movements.
The doctor will instruct the patient to fixate at the farthest point on the card and say how many lines they can see and whether the lines cross at the fixation point. S/he might move the fixation point closer to the patient until they see two parallel lines. However, if the patient has a suppressed eye, they will only see one line. The doctor may repeat the test several times.
In a patient with good convergence ability, both tests have similar results. The average NPC is about six to ten centimeters for healthy eyes and the convergence recovery point may be up to 15 centimeters. If the NPC exceeds ten centimeters, it may indicate weak convergence. Patients with a convergence disorder who engage in intense reading and long hours of near work may have a convergence recovery point that is over 15 centimeters.
Convergence insufficiency is a neuromuscular and sensory abnormality and treatment aims at changing the visual-neural links responsible for convergence. Generally, there is no need for treatment if the patient has no symptoms. Where the patient displays signs, the doctor may recommend treatment to increase eye convergence and improve or eliminate the anomaly. The treatment will depend on the patient's age and preference. The treatment may include:
- Computer vision therapy
- Pencil push up exercises
- In-office exercise
- Reading glasses
Usually, pencil pushups are the first line of treatment for CI. Computer vision therapy is more effective for young adults and kids. Reading glasses only provide a temporary solution and surgery is rarely recommended.